The size of a dehumidifier is usually determined by the amount of moisture it extracts from the air in a 24-hour period. The Association of Home Appliance Manufacturers' guidelines are a good resource in deciding on a correctly sized dehumidifier. Portability is also important, especially for dehumidifiers that will be used in multiple rooms. Ideally, the unit should be lightweight, compact and have rolling casters or carrying handles.

A built-in humidistat is a good feature to have because it...

There are a few advantages of owning a whole house humidifier. A whole house humidifier would be able to keep the entire house in a humid condition which is not something that a small portable humidifier can do. 

Having a whole house humidifier is convenient in the sense that you don't have to refill and maintain many portable humidifiers. Rather than spending money buying a few portable humidifiers and placing them all around the house, you should get a whole house humidifier to do the work. ...